The present invention relates to a charged coalescer type oil-type water separating apparatus which efficiently separates water from water-containing oil or oil from oil-containing water to enable their recycling and which contributes to not only saving of resources and energy but also cleaning of the earth environment by reducing waste oil and liquids.
To prevent the earth environment from being polluted, strict regulations on the release of waste oil and liquids to the natural environment have been established in recent years. These regulations require to reduce the total amount of waste oil and liquids and, therefore, it is an urgent subject to separate and collect water and oil from water-containing oil and oil-containing water. The separation and collection of water and oil from water-containing oil and oil-containing water is also required for the purpose of saving resources and energy, which is another important issue.
Among oil-water separating apparatuses, a coalescer type apparatus is well known. The coalescer type oil-water separating apparatus uses a coalescer type filter element in which filtering materials are different in mesh size and are layered such that meshes become finer in a step-like manner toward the downstream side in the fluid passing direction. The most general form of this type of oil-water separating apparatus is as follows. A cylindrical coalescer type filter element is disposed at the center of a container, and a pressurized liquid to be processed is introduced into the container from the outside and passed through the filter element from its outside to inside. While the liquid is passed through the filter element oil particles are interrupted by meshes that become finer in a step-like manner in the liquid passing direction, and caused to go up. Water thus separated is extracted from the axial portion of the filter element.
Another oil-water separating apparatus is known which was proposed in Japanese Patent Application No. Hei. 1-213168 entitled "Two Liquid Separating Methods and Apparatuses for Implementing them"filed by the present applicant. This apparatus has the following configuration. A single layer cylindrical filter element having meshes of an uniform size over the entire area is disposed at the center of a cylindrical container also serving as an outer cylinder grounding electrode. A central cylinder electrode having the same potential as the outer cylinder grounding electrode is placed at the axial position of the filter element. On the other hand, a cylindrical charge electrode made of a perforated metal plate is disposed outside the filter element so as to contact with its outer surface, and a voltage that can lower or eliminate the zeta potential of impurity particles in a liquid being processed is applied between the cylindrical charge electrode and the outer cylinder grounding electrode and between the cylindrical charge electrode and the central cylinder electrode. In this apparatus, a pressurized liquid to be processed that has been introduced into the container from the outside is first passed through an oil-water separating space formed between the cylindrical charge electrode and the outer cylinder grounding electrode in which space oil particles cohere due to the charge effect and oil goes up. i.e., separated, due to the difference in specific gravity. Then the separated water is passed through the filter element from its outer surface to its axial portion, and a filtered liquid is discharged from the filter axial portion.
However, each of the above two apparatuses still has problems to be solved.
The oil-water separating apparatus using the coalescer type filter element, in which the oil-water separation relies on only the physical operation, i.e., the interruption of oil particles by meshes of the filter, has a limitation in the size of separable oil particles. For example, where oil is in the form of emulsion, filter meshes need to have a very small size of less than 1 micron. Since such a filter tends to clog up early due to inclusion of dust or oil having a high viscosity, the filter element needs to be replaced at a high frequency. That is, in the conventional coalescer type oil-water separating apparatus, the running cost inevitably increases to obtain a higher accuracy.
In the two liquids separating apparatus proposed in the Japanese patent application of the present applicant, a liquid to be processed is placed in an electric field. Therefore, impurity particles and oil particles are caused to cohere to become coarser due to the charge cohesion effect, to thereby provide the filtering effect and the oil-water separating effect which are superior to those of the coalescer type oil-water separating apparatus. However, since meshes of the filter have a uniform size over the entire area, the apparatus of the present applicant cannot provide an improvement in the effect that impurity particles and oil particles cohere to become coarser due to a step-like profile of mesh sizes, as is expected in the coalescer type filter element.
Further, in the latter apparatus, a liquid to be processed is first subjected to oil-water separation, only the separated water is then filtered by being passed through the filter from its outer surface to its inside, and finally the filtered separated water is discharged from the filter axial portion. Therefore, dust and the like are not eliminated from the separated oil. To reuse the oil thus separated and collected, it is necessary to install a separate filtering device outside the oil-water separating apparatus.